Entecavir (entecavir or BMS-2000475) which has inhibited effect on polymerase of hepatitis B virus (HBV) is analogues of 2 cyclopentyl deoxyguanosine. Entecavir's chemical name is referred to as [1S-(1α, 3α, 4β)]-2-amino-1,9-dihydro-9-[4-hydroxy-3-hydroxymethyl]-2-methylenecyclopentyl]-6H-purin-6-one, and its molecule structural formula has the following general formula (I):

Entecavir could be converted to an active entecavir triphosphate by phosphorylation. Entecavir triphosphate could compete with triphosphate deoxyguanosine which is a natural substrate of HBV polymerase to inhibit activities of viral polymerase (reverse transcriptase). Entecavir exhibits much times stronger effects than Lamivudine in experiments such as antiviral activities, resistances, cross resistances and the like.
Many methods of preparing for entecavir compounds and a method for obtaining a little entecavir solid separated by resin column chromatography are described in U.S. Pat. No. 5,206,244 and WO98/0994. The method of preparing for non-crystalline forms of entecavir is disclosed in Chinese Patent Publication No. CN1660846A. But the crystalline forms of entecavir and its performances are not researched and reported in the above-mentioned patents.
In recent years, drug polymorphism is increasingly becoming indispensable and important constituents in the processes of drug researches and quality controls of drug production, and causes more and more people's concerns in the pharmaceutical fields. To carry out the research of drug polymorphism is helpful to bioactivity choices of new drug compounds, is helpful to enhancements of bioavailability to promote clinical effects, is helpful to choices and designs of drug administration route and determinations of technological parameters of pharmaceutical preparation to enhance quality of drug production. Different crystal forms of the same drug may have significant differences in bioavailability. Certain crystal form may have higher bioactivity than other crystal forms of the same drug.